Charles Tapley Hoyt

https://www.uniprot.org/docs/subcell.txt

http://prot-shiny-vm.broadinstitute.org:3838/ptmsigdb-app/

https://github.com/cBioPortal/oncotree/blob/master/scripts/ontology_to_ontology_mapping_tool/ontology_mappings.txt

ICDO Xrefs

1

Okay they're not really xrefs, since it claims the relationship is "related to", but since this file is hidden in an NCI FTP server, maybe nobody ever saw it before...

See list on https://github.com/ropensci/webchem

Many Wikidata equivalences are listed through the "exact match" property rather than through properties specifically referring to identifiers from a given resource. Get them!